This invention relates to intake and exhaust valves and an intake port in an internal combustion engine, and more particularly to an improved structure of a valve spring retainer or shoe and an improved shape of the intake port in the internal combustion engine.
In general, in order to increase a combustion efficiency of an internal combustion engine, a valve spring retainer must be designed properly to open and close accurately intake and exhaust valves, an intake port must be properly designed to enhance an intake efficiency and an enlarged spiral vortex in the axial direction of a cylinder must be generated. Thus, contact between air and fuel in the combustion chamber is enhanced.
In these countermeasures, a conventional structure of the valve spring retainer of each of intake and exhaust valves is shown in FIGS. 9 to 11. In FIG. 9, a cylinder head 1 has two valve guides 3, 3 therein for guiding the valve stems 8, 8 of intake and exhaust valves V.sub.1, V.sub.2 so as to be moved in their axial direction. Each valve stem 8a, has at its upper portion, a cut portion 5 which is engaged with a valve spring retainer 80 via a pair of split cotters 41a, 41b. Two valve springs 9, 9 are held between a cylinder head 1 and each valve spring retainer 80, and the distal end 40 of each of rocker arms abuts against the upper end of each valve stem 8a to move each valve stem 8a upward and downward against the spring force of each valve spring 9 thereby to open and close two opening portions 60, 60 of intake and exhaust ports K, H with two valve portions 8b, 8b abutting against two valve seats 2,2, respectively. The cotters 41a, 41b are inserted into a tapered hole 80a of each valve retainer 80 while holding the cut portion 5 of the valve stem 8a therebetween as shown in FIGS. 9 to 11. The cotters 41a, 41b are in the shape of a wedge and have tapered surfaces T.sub.s, T.sub.s, respectively. Therefore, if accuracy of finishing for the valve retainer 80 and the cotters 41a, 41b is not good, for example, those members may be assembled in a state shown in FIG. 12 wherein the cotters 41a, 41b are located in a raised position from a normal position. In this case, the valve spring 9 is compressed by a bigger force than a normal force. That is, a bigger force is necessary for opening the opening portion 60 by lowering the intake valve V.sub.1 with the rocker arm 40. Therefore, the compressed length of the valve spring 9 (a force exerted on the intake valve V.sub.1 by the valve spring 9) is not uniform to differentiate the repulsive force of the valve spring 9 from its design value. This causes various problems.
Further, with respect to the shape of the conventional intake port, a lateral path member 6 for the intake port K with a simple uniform circular section (FIGS. 12, 13) is disposed perpendicularly to the center axis C--C of the cylinder head 1. Therefore, tumbler flow lacks velocity of component in the direction of the center axis C--C of the cylinder head 1, and the sectional area of a connecting portion S between a lateral path 61, provided in the lateral path member 6, of the intake port K and a vertical path 62 connected to the inner end of the lateral path 61 and accommodating the lower portion of the valve stem 8a is small to decrease intake efficiency of admission of a mixture of fuel and air thereby to cause various problems.